Scrutinizing what might be gently called the bane of procreation, researchers have made new discoveries about a subject returned to widespread public consciousness in the current baby boom--vomiting in pregnancy.

And in the process of defining the relative risks--and what emerge as the clear benefits--of such an unpleasant experience, the researchers have confirmed observations that the condition, especially in the first trimester, doesn't originate in a woman's head. It does, indeed, come from somewhere else, and is largely tied to a woman's hormonal makeup.

The problem affects more women than it spares: One study said that 56% of pregnant women reported vomiting and another survey found that 70% experienced vomiting and nausea.

It has been many years since doctors first recognized that the term "morning sickness" was a misnomer and that the reality is that the problem in early pregnancy honors no daily time schedule.

And now, researchers working independently at the federal government's National Institute of Child Health and Human Development in Bethseda, Md., and at UCLA have made these additional observations:

--A greater proportion of women experiencing their first pregnancies vomit than those in second and subsequent pregnancies. But a woman who has the problem in a first pregnancy is more likely to continue to have it in later ones than a woman who does not have it initially. There is no statistically significant difference in experiencing the problem between women who planned to become pregnant and those who did not.

--Significantly, vomiting in pregnancy was clearly associated with a decreased risk of miscarriage or stillbirth and women who went through the unpleasantness were less likely to deliver prematurely. There was no statistically significant difference in birth weight between babies of women who vomited and those who did not.

--Younger women--especially those under 20--are more likely to vomit than older ones. Women over 35 have the problem least.

--Better educated women have fewer such symptoms than those whose education stopped before they graduated from high school.

--Non-smokers vomited more than smokers, but the researchers quickly emphasized that smoking, itself, does not appear to be protective. Rather, women who can tolerate noxious cigarette fumes are by nature apparently less prone to nausea and vomiting.

--Black women and other minority group members vomited more than Anglos and the problem was much more common among women with excessive weight--particularly those weighing 170 pounds or more. Vomiting was more common among women who were going to have twins or other multiple births than it was among women carrying only a single fetus.

--Women who had histories of one or more years of infertility were at decreased risk of vomiting when they finally got pregnant. This was especially true of women who had taken Clomid, a drug that encourages ovulation.

--Women who work as homemakers appeared to have a significantly increased risk of vomiting. However, researchers said this appeared to be because housewives tend to be nonsmokers, nondrinkers and nonwhite in greater proportion than women employed outside the home.

Two Separate Studies

The new observations were based on two separate studies, conducted independently--although both research teams are acquainted and generally concur with one another's findings. The government study was published in this month's issue of the journal Obstetrics and Gynecology. The UCLA research was done in preparation of a doctoral thesis by M. Margaret Weigel, a Portland, Ore., biological anthropologist.

The government study, led by Dr. Mark Klebanoff, analyzed data from 9,098 first trimester medical records collected during the Collaborative Perinatal Project, a study that ended its data gathering in 1966 after analysis of 56,000 pregnancies starting in 1959. Klebanoff said he and other researchers on the team believe that conclusions from the data are apparently as accurate today as they were when the information was collected.

The assertion got support from Weigel, whose ULCA study agrees on virtually all major points with the government analysis. Weigel conducted interviews with 903 women who were patients at UCLA during the last five years.

Klebanoff and Weigel agreed that an underlying conclusion of both studies is that they significantly substantiate earlier theories that vomiting in pregnancy has little, if anything, to do with a woman's anxiety about pregnancy. Instead, both researchers agreed, the condition's likelihood is determined by hormonal concentrations in the body that a woman is powerless to change.

Acute Stress Problems

Weigel did find, however, that women who were caught up in acute stress situations, like the breakup of a relationship or serious financial hardship when they became pregnant had a greater incidence of vomiting. The acute stress problem remained a risk factor for vomiting not just in the first trimester, but throughout the pregnancy.